Yellow Canopy Syndrome trigger remains unclear

Yellow Canopy Syndrome trigger remains unclear

After five years without an answer, scientists are continuing their research across cane growing regions in the north to try and crack the elusive cause of Yellow Canopy Syndrome (YCS).

YCS impacts sugar cane in a number of ways. This can range from yellowing in one or two leaves to yellowing right through the canopy. Depending on the degree of symptoms, crop growth can be compromised with potential impacts on final yields.

There are currently more than 30 researchers working on YCS in some capacity, approaching the problem from different angles and across four projects in multiple locations.

The funding for the projects has been delivered by Sugar Research Australia (SRA) and although Manager of Strategic Initiatives at SRA, Dr Frikkie Botha said a number of possible causes of the condition have been largely eliminated from further consideration, the root cause is still unknown at this point in time.

“There is research being conducted at laboratories at SRA in Brisbane, the Western Sydney University, and in laboratories in other locations around Australia and overseas,” Dr Botha said.

“There is also a wide range of coordinated and collaborative field and pot trials occurring in 2016 at many locations including in the Burdekin, Ingham, Mackay, Proserpine, and Mulgrave,” he said.

Dr Botha said SRA is collaborating with both growers and productivity services organisations with some of these trials.

“The research focus is on all the known plant nutrients, metabolites and diseases as well as a broad deep sequencing to identify any novel micro-organisms that might show significant increases during YCS development.

“Although no causal agent has yet been identified, many factors such as macro and micronutrients and some of the known sugarcane diseases have been ruled out. In addition, we have also rules out factors such as Nigrospora as a cause.”

He said there is no simple tool for YCS diagnosis yet, but that SRA has made this a priority.

“We’ve observed several parameters that appear unique to YCS. These include the silica to magnesium ratio, chlorophyll fluorescence, starch and sucrose. But a firm pattern is yet to be established.”

No varieties of cane are immune to YCS either, although there is variation between varieties in how they express the symptoms.

“It’s important to realise that some varieties ‘hang on’ to the older leaves for longer and hence always look to be affected more. KQ228A is an example of a variety that appears more susceptible for this reason.

“Following a recent review of SRA’s YCS research investment, SRA will strengthen the focus on variability of variety responses with an evaluation of the potential for breeding and selection for resistance.”

YCS was first detected in several crops of cane in the Mulgrave Mill area, just north of Cairns in 2012. Since that first occurrence YCS has been observed in all regions north of and including Plane Creek.

“The severity can vary greatly between regions and within regions and their aren’t any obvious correlations between YCS and soil type or weather that have been found, however SRA is continuing to investigate these factors through multiple trials across impacted regions.

He said the exact impact – and therefore the economic impact – is difficult to precisely quantify.

“In the worst cases, YCS has been observed to reduce yield by 40 per cent or more, which is a very devastating impact for those growers suffering that degree of crop loss.

“In other cases, the impact is less severe and crops have recovered by harvest.”

Collaboration key to solving YCS puzzle

Ian Shepherdson has been growing cane in the Burdekin since 1992 and was one of the first growers effected by YCS in the region in October, 2012.

“When I first saw it, I didn’t pay much attention I thought it might have just been caused by poor soil,” Mr Shepherdson said.

It wasn’t until it got really rampant in my crop around January 2013 that I realised I had a big problem on my hands,” he said.

He said in that 2012-13 period 100pc of his crop was effected by YCS, with approximately 50pc moderately effected and the other half severely impacted.

“My last ratoons were particularly bad, I only attained about half of my usual yield and lost $100,000 easily.

“YCS is still here in bad numbers, though it took a month longer than usual this year to explode visibly in my crop.

“Even though it’s widespread again on my farm, the yield impact won’t be as severe as we’ve had reasonable growth until now.”

In an effort to find an answer for the YCS problem Mr Shepherdson gave Dr Botha and the SRA research team the go ahead to conduct trials on his property.

“I’d been communicating with SRA pretty much since the first case of YCS appeared here, Dave Olsen approached me to ask if I’d like to collaborate with them to find some answers to the problem.”

Three trials are currently being conducted at Mr Shepherdson focusing on the link between crop age and incidence of YCS; a management trial to find if YCS is aggravated or mitigated by using different treatments including lime, gypsum, mill mud and Six Easy Steps fertiliser and a pathology trial is being carried out to establish if YCS is caused by a virus.

“The SRA blokes have been really good to work with, and even though it’s frustrating not having an answer yet, it must be equally frustrating for them when no answers are coming easy.”

When asked to hazard his own guess as to what he thinks might be the cause of YCS, Mr Shepherdson said he thinks it’s a disconnect between plants and their roots.

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